Air/fuel ratio control means for dual fuel burners

ABSTRACT

An improvement in a gas/oil burner substantially increases the turn down ratio. An improved air damper structure and linkage of the damper to a fuel ratio control opens the damper only at moderate fuel infeed rates. The damper remains closed at low fuel infeed rates and leakage around the damper supplies adequate air for good combustion and permits oil firing rates lower than in known burners of the type described.

United States Patent 1191 [111 3,869,243

Creuz Mar. 4, 1975 [5 AIR/FUEL RATIO CONTROL MEANS FOR 1,955,661 4/1934 Waldo 123/119 DB DUAL FUEL BURNERS 3,450,115 6/1969 TOda et a1. 123/119 DB [75] Walter R. Creuz, Chatham, NJ.

Assignee: Aero-Flow Dynamics, Inc. (The Wing Company Division), Linden, NJ.

Filed: Nov. 2, 1973 Appl. No.: 412,483

Inventor:

U.S. Cl 431/90, 137/99, 239/61,

431/12, 126/285 Int. Cl. F23n 1/02 Field of Search 431/12, 90; 137/99; 239/61; 74/513; 123/119 D, 119 DB; 126/285 References Cited UNITED STATES PATENTS 1/1915 Farrell .1 123/119 DB Primary Eraminer-Edward G. Favors Attorney, Agent, or FirmBrooks., Haidt & Haffner 7 Claims, 3 Drawing Figures .23 I5 La '20 1 t Z5 Z7 11 I a 4'2. 43 @Q a 1 2| i 44' 345 (3 4| m- ?b 9 56 35 1 ii: 32 v Q 46 1 a1 25 Q AIR/FUEL RATIO CONTROL MEANS FOR DUAL FUEL BURNERS BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to gas/oil burners and more particularly to an improved air damper and damper actuation linkage for controlling the primary combustion air intake when firing on either oil or gas.

2. Description of the Prior Art Gas/oil burners are widely used for air heating and furnace applications and so-called self-contained gas- /oil burners offer particular advantages in industrial heating operations.

U.S. Pat. No. 3,574,508 relates to an internally fired industrial gas burner having a control linked to two interconnected butterfly valves, one of which valves regulates the flow of gas into a mixing chamber, the other valve regulating the supply of air to the mixing chamber. The valves are positively linked so that for any degree of opening of the gas valve there is a corresponding opening of the air valve.

Despite this and other attempts to provide a proper ratio of gas to air throughout a wider working range of burners having a positive linkage between air feed regulation means and fuel regulation means it has been found that at low fuel feed rates there is ordinarily an excess amount of air, especially when the fuel is oil. In arrangements in which any opening of the fuel regulation means has a corresponding opening of the air regulation means the operating range is limited because of the excess air feed at low fuel inputs. Typically the turn down ratio, i.e., the ratio between the maximum fuel infeed rate and the minimum fuel infeed rate for satisfactory operation of such burners is less than to I.

SUMMARY OF THE INVENTION The present invention provides a substantially larger turn down ratio in self-contained dual fuel burners of the type used in industrial heating applications by means of an improved control linkage and an improved air regulating damper. The invention may be applicable to various kinds of burners in which a ratio between fuel and air entering a mixing chamber must be controlled, but for purposes of illustration the invention is described as applied to a burner of the type described in the aforementioned U.S. Pat. No. 3,574,508, which is a self-contained burner in which a blower forces air into a conical chamber for mixing with fuel. In the embodiment described the linkage of the invention couples an air feed damper with a valve for regulating the fuel feed so that the fuel feed valve must be opened to a predetermined extent before the damper is actuated toward an open position. Thus at low rates of fuel input the damper remains closed and sufficient air leaks around the damper to promote good combustion of the fuel. When oil is being fired, odors indicative of inadequate combustion are absent throughout the increased operating range of burners employing the improvement of this invention, and good combustion to gas fuel is noted throughout the range of operation.

The damper is a plate having leading and following edge portions bent in the direction of opening of the burner for tighter sealing of an air passage, to minimize, although not to completely eliminate, air leakage around the damper when in closed position. The damper has a slotted cam opening by which it is linked to the respective fuel valves, providing lost motion so that the damper will not respond to initial movementof either the gas or the oil fuel valves, but will begin to open only when either of the fuel valves has achieved approximately thirty degree opening.

The improved damper and linkage of the invention result in an increase in the turn down ratio of burners employing the invention. In a typical embodiment, modification of a dual fuel burner to incorporate the improvement of the invention improved the turn down ratio from about 9 to l to about 18 to I.

These and other features and advantages of the improvements of the invention will be more fully understood from the following detailed description of the invention, especially when the description is read in conjunction with the accompanying figures of the drawing showing a currently preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a somewhat schematic illustration of a burner embodying a control mechanism according to the invention.

FIG. 2 is a detail view in perspective of an arrangement for linking valves controlling oil and gas flow with a damper for controlling the admission of combustion air in accordance with the invention.

FIG. 3 is a detail view in perspective of a damper according to the invention.

DETAILED DESCRIPTION OF THE PREFERRE EMBODIMENT 1 FIG. 1 illustrates the embodiment of improvements according to the invention in a burner 10 adapted for industrial process heating. The burner 10 would normally be used in combination with an oven or baking chamber (not illustrated) which would receive hot gases from a fuel-air mixing and ignition chamber shown in the drawing as a cone 11. The invention is primarily directed to the control of the ratio of fuel to air fed into, mixed and ignited in the cone 11. The cone 11 or other suitable mixing and ignition chamber can be of any suitable construction conventionally used in burners of the type described, for example, as shown in U.S. Pat. No. 3,574,508, the disclosure of which patent is hereby incorporated by reference.

For simplicity of illustration FIG. I shows the chamber ll supplied with gaseous fuel by way of fuel infeed means generally designated by the reference numeral 112, but it will appear in the discussion relating to FIG. 2 that the invention is contemplated to apply to burners employing liquid and/or gaseous fuels and having conventional pilot burners.

In any case the conical chamber I1 is also supplied with air for combustion of the fuel fed into the chamber. The cone III is supported within a housing 13, which is generally cylindrical in shape, and as shown in FIG. 1 a blower 14 for the introduction of combustion air compresses a fan l5 mounted in a housing 16 secured above and communicating with the interior of the housing 13. The fan 15 is shown adapted to be driven by a motor 17 also mounted on the housing 13.

The housing 16 of the fan 15 provides an internal duct 20 for passage of forced air to the interior of the cone housing 113, whence the air can enter the cone 11 through entry means, here shown as holes 21 through the cone 11, to mix with fuel fed into the interior of the cone 11.

The blower 14 with its motor 17 and fan are preferably of the constantly operating type, so the fan 15 under normal operating conditions will continuously force air downward towards the duct 20.

In order to control the flow of combustion air to the interior of the conical chamber 11, a damper 22 is pivotally mounted within the duct 20 to close or partially or fully open the duct 20 for the flow of combustion air into the interior of the housing 13 and thence to the cone 11 for mixing with the fuel.

As further shown in FIG. 1 the damper 22 is pivotable about an axis 23 and has a downwardly extending car 24. Riding in a slot 25 of the car 24 is an end portion 26 of a generally vertical rod 27 for opening and closing the damper 22. The rod 27 has a limited degree of up and down motion without moving the damper 22 since its end portion 26 can slide up or down the length of the slot 25 without moving the damper 22 and this last motion provides for improved control as will further appear in the discussion of the operation of the improved burner.

The rod 27 extends downwardly alongside the cone 11 and its lower ends 28 is suitably connected to means for converting rotational motion to verticle straight line movement here shown as a bell crank 30 having a pivot point 31, and arms 32 and 33, the arm 33 being pivotally connected to the bent lower end portion 28 of the rod 27. The arm 32 of the crank 30 is pivotally connected to a bent portion 35 of a generally horizontal linking rod 36 to couple the motion of the damper 22 to that of metering means for the combustion fuel fed to the cone 11.

One kind of fuel infeed means 12, as illustrated in FIG. 1, comprises a supplyline 40 leading upwardly to a hollow space 41 formed at the rear ofthe housing 13.

The space 41 opens toward the narrow end 42 of the cone 11 through a duct 43 having a nozzle 44 for introducing fuel from the duct 43 to the cone 11 through apertures 45. It willbe seen that valve means, here shown as a butterfly valve 46 with its disc 47 pivotally mounted within a narrow portion 48 of the supply line 40 to meter the fuel fed to the space 41. The axle 53 of the valve 46 is coupled to the linking rod 36 for pivotal motion upon generally horizontal movement of the linking rod 36.

The butterfly valve metering arrangement shown in FIG. I is particularly suitable for controlling the supply of gaseous fuel such as a hydrocarbon gas to a burner chamber such as the cone 11 shown.

The linkage just described will be more fully understood by reference to FIG. 2 of the drawing, wherein the housing 13 and certain other fixed structures have been omitted for the sake of clarity.

As shown in FIG. 2, the bell crank 30 is fixedly secured at its pivot point 31 to a shaft 51 for rotation with the shaft 51. Beyond the bell crank 30, the shaft 51 continues to a liquid fuel metering device generally indicated by the reference numeral 52. Attention is first directed to the gaseous fuel feed control means 12 shown at the right in FIG. 2 and already discussed with respect to FIG. I. It will be seen that an axle 53 of the butterfly valve in the gas supply line 40 has one end 54 of a crank arm 55 fixedly secured thereto, the other end 56 of the crank arm pivotally receiving a bent end portion 57 of the linking rod 36. Accordingly, rotational motion of the bell crank 30 isdirectly transmitted to and converted to rotational motion of the axle 53 of the butterfly valve 46. Corresponding to the pivoting of the butterfly valve there is a vertical translational motion of the rod 27, which with some lost motion, operates the air damper 22.

Suitably, one end of the shaft 51 is connected to means (not shown) such as a control knob for manual control or an automatic control mechanism for turning of the shaft 51 to rotate the butterfly valve and, upon sufficient rotation of the shaft 51, the air damper 22 as well. In the embodiment of FIG. 2 this control knob or automatic control device could act directly on the shaft 51, or, preferably turn the shaft 51 through rotation of parts of the device 52.

Referring now to the left-hand portion of FIG. 2, a suitable metering device for liquid fuel can be seen to comprise a piston valve and camming surface arrangement generally indicated by the reference numeral 52, and coupled to the same shaft 51 as the previously described gas control means. The assembly illustrated in FIG. 2 is thus adapted to use in a so-called dual-fuel burner which operates on either oil or gas. It should be understood that either the liquid fuel control means 52 or the gascontrol means 12 could be omitted in a single fuel burner application while retaining the operating parts which pertain to the single fuel employed.

FIG. 2 shows a feed line 60 for a liquid fuel such as fuel oil to a metering valve 61 of the piston type with a spring loaded piston 62 for controlling the rate of flow of liquid fuel out through the outlet line 63. The valve 61 can be of any suitable known type which meters the flow of liquid in response to the position of a piston. The piston 62 has its outer end 63 in contact with a slanted camming surface 64 of a sector-shaped member 65 that is mounted for rotation with the shaft 51. The sector-shaped member 65 is shown in FIG. 2 in an intermediate position, i.e., a position at which the flow of fuel through the valve 61 would be at a moderate rate. Rearward movement of the sector-shaped member will increase the rate of fuel flow; and forward movement, that is, movement toward the viewer of the drawing, will decrease the fuel flow, since the camming surface will press the piston inward as the sectorshaped member 65 is moved forward. Suitable indicia can be associated with the member 65 to indicate the position in which the valve has been set.

Since the shaft 51 is fixed to the sector-shaped member 65 for rotation therewith the shaft can be turned, and through the linkage already described, the fuel and air flows can be regulated by moving the member 65 to a desired position. This could be done manually or through an automatic actuating mechanism coupled with equipment associated with the burner, for thermostatic control or some other appropriate purpose.

It will be understood from the foregoing description that the liquid fuel inlet 60 and the gaseous fuel intake line 40 are not operative at the same time, and that appropriate check valves to open or close these fuel lines must be provided in a dual fuel burner of the type described.

Reference is now made to FIG. 3 showing the improved damper of the invention. Unlike the dampers conventionally used the damper 22 is not a simple flat plate sized to fit the rectangular cross-sectional area of the duct 20. The damper 22 has a flat body '70 with lateral edge portions 71 and 72 uniformly bent to form obtuse angles in opposite directions with respect to the body 70. Reverting to FIG. 1 it will be seen that a leading edge 71 is directed generally upward when the damper 22 is in a closed position while the following edge 72 is generally downwardly directed.

In a damper having a width of about 5 inches, the edge portions can suitably each be about inch wide. Suitably the angle formed between each edge portion 7]. or 72 and the damper body 70 is somewhat less than 120, preferably about 1 10. When the damper 22 is in a closed position, closing the duct 20, the leading and following damper edges 71 and 72 form a better seal described, incorporating the improvements of this inagainst leakage than is provided by a plain flat plate,

although some air, driven by the powerful fan will leak past the damper 22. Slots 73 and 74 are shown for the reception of pin means upon which the damper can be turned. The member 75 is an angle attached to the underside of the damper body 70, for example, by spot welding of a short leg 76 of the angle 75 thereto. The longer leg 24 of the angle 75 extends perpendicularly to the damper body 70 and has a slot-like hole 25 for the reception of the end portion 26 of the rod 27 shown in FIG. 1. The rod end 26 is free to slide in the slot 25. However, because of aerodynamic considerations, the damper 22 will always tend to move toward its closed position or to stay in closed position unless urged up- ,wardly by pushing force of the rod end 26 against the upper end of the slot 25. Accordingly, unless the damper is in a closed position, the rod end 26 will always be at the upper end of the slot 25.

A suitable turning movement is provided if the angle 75 is located a small distance away from the longitudinal centerline of the damper body 70. Thus, in the typical damper about 5 inches wide, the center of the angle 75 can be about three-fourths inch away from the axis of rotation of the damper 22.

Operation In a conventional burner in which the fuel metering valve and air damper are linked for concordant opening and closing movement the linkage is positive with no lost motion. On the contrary, the sliding fit of the rod end 26 of the linkage of this invention in the slot 25 permits some lost motion.

When the burner is to be turned on by feeding of either liquid fuel or gaseous fuel into the cone 11 through either valve 52 or valve 46 the fan 15 will be operating when the valve is opened, but the air damper 22 will not be immediately actuated to move towards an open position. During the initial opening of the valves and resulting rotation of the shaft 51 and bell crank 30, the rod 27 is free to move upward to an extent equal to the length of the slot 25 before the rod end 26 engages the upper end of the slot 25 and begins to push the damper open. Thus, for low rates of fuel feed, the only air available for combustion is that which is already present in the cone 11 or that leaks past the closed damper 22. It has been found that contrary to what might be expected, this leaked-in air is completely adequate for very effective combustion of the fuel at low fuel feed rates, and that immediate opening of the damper as in conventional burners is not only unnecessary but is actually disadvantageous. Opening of the damper at low fuel intake rates permits the entry of air in excess of that needed for thorough combustion of the fuel and can actually result in incomplete combustion. Incomvention as shown in FIGS. I3 and already described. Burner B differed in that its damper was a'plain flat plate without bent endge portions, and accordingly somewhat smaller than the damper 22. Instead of a slot 25 the angle on the damper of burner B had a round hole permitting only pivotal motion of the upper end of rod 27. Accordingly, the damper of burner B started to open as soon as the fuel valve was opened to any extent whatever. The slot 25 of burner A permitted fuel valve 52 to be turned about 30 from its. fully closed position before the damper 22 was actuated to opening movement.

With the exception of the differences just noted, both burners A and B were the same. The burners were operated with oil and had interrupted gas pilot flames. The operation of burners with such pilots is known and need not be discussed here in detail since the main fuel operation is what is compared. The rates of feed of main oil are given in gallons per hour (GPH).

Burner A incorporating the improvements of this invention performed well at oil feed rates from a minimum of 1 GPH to a maximum of 18 GPH. No odor was detected throughout this range and the fire was clean indicating thorough fuel combustion. The damper remained closed at settings of the oil valve up to 4 GPH, at settings from Ste 7 GPH the damper 22 rotated from about 10 to about 20, to provide the amount of air required at these firing rates. At higher rates the damper opened still further.

Burner B, without the improvements of this invention was a model 525 burner marketed under the trademark OVENPAK by Maxon Corporation of Muncie, Ind. The manufacturer rated the minimum capacity, i.e., fuel infeed rate, at 2.25 GPI-I of fuel oil. At rates of fuel feed between this minimum and 8 GPH oil odor was present, indicating incomplete fuel combustion. Even if this odor and fuel waste cam be tolerated, the turn down ratio between a minimum of 2.25 GPH and a maximum of 18 GPH is less than 9 to 1.

With the improved burner according to the invention, a good operating range with no oil odor, of 1 GPH to 18 GPH provides a turn down ratio of 18 to 1.

Additional tests were conducted using gas as the fuel and similar results were obtained, again showing the superiority of the burner improved in accordance with this invention.

Certain modifications, adaptations and substitutions of equivalents will suggest themselves to those acquainted with the art and are considered. to be within the spirit and scope of the invention.

What is claimed is:

1. In a burner of the type having a combustion chamber, fuel inlet means and air inlet means for admission of fuel and air to the combustion chamber, metering valve means in said fuel inlet means and damper means in said air inlet means, and a linkage between said metering valve means and said damper means, the improvement comprising means permitting lost motion in said linkage for permitting said metering valve means to be partially opened while the damper means remains closed and for opening said damper means only after said metering valve has been opened to a predetermined extent.

2. The improvement of claim 1 wherein said lost motion means comprises slot means slidably receiving rod means of said linkage for allowing travel of said rod means in said slot while said damper means remains closed.

3. In a burner of the type having a combustion chamber, fuel inlet means and air inlet means for admission of fuel and air to the combustion chamber, metering valve means in said fuel inlet means and damper means in said air inlet means, and a linkage between said metering valve means and said damper means, the improvement comprising means permitting lost motion in said linkage for permitting said metering valve means to be partially opened while the damper means remains closed and for opening said damper means only after said metering valve has been opened to a predetermined extent, said damper means comprising a flat generally rectangular damper body, a leading edge portion bent at an obtuse angle with respect to said body and a following edge portion bent at an obtuse angle with respect to said body; said edge portions being bent in opposite directions with respect to said body.

4. The improvement of claim 3 wherein said fuel inlet means includes a gaseous fuel supply line and a liquid fuel inlet line, the metering valve means comprising a valve in said gaseous fuel supply line and a second valve in said liquid fuel inlet line, said valves being coupled for concordant actuation.

5. A linkage for coordinating the opening of an air damper in a burner with the opening of two fuel supply valves comprising shaft means coupled to said fuel supply valves for rotation corresponding to opening and closing motion of the valves, crank means fixed on said shaft means, a linking rod pivotally secured at one end to said crank means, the other end of said linking rod being slidably and pivotally received in a slot defined in means fixed to said air damper for limited movement of said linking rod while the air damper remains stationary, one of said valves being actuated by the rotation of a member having a camming surface in contact with a piston of said one valve.

6. The linkage of claim 5 wherein said means fixed to said air damper is an angle having a leg extending generally perpendicular to a body portion of said damper, said slot being defined in said leg.

7. An air damper for a burner having a flat rectangular body, and two opposite edge portions integrally formed with said body and extending parallel to the axis of rotation of said damper, each said edge portion being bent to form an obtuse angle with respect to the plane of said body, said edge portions extending in generally opposite directions with respect to said body, and means secured to said body and having a leg extending generally perpendicular to said body, said leg means defining a slot extending generally perpendicular to said body. 

1. In a burner of the type having a combustion chamber, fuel inlet means and air inlet means for admission of fuel and air to the combustion chamber, metering valve means in said fuel inlet means and damper means in said air inlet means, and a linkage between said metering valve means and said damper means, the improvement comprising means permitting lost motion in said linkage for permitting said metering valve means to be partially opened while the damper means remains closed and for opening said damper means only after said metering valve has been opened to a predetermined extent.
 2. The improvement of claim 1 wherein said lost motion means comprises slot means slidably receiving rod means of said linkage for allowing travel of said rod means in said slot while said damper means remains closed.
 3. In a burner of the type having a combustion chamber, fuel inlet means and air inlet means for admission of fuel and air to the combustion chamber, metering valve means in said fuel inlet means and damper means in said air inlet means, and a linkage between said metering valve means and said damper means, the improvement comprising means permitting lost motion in said linkage for permitting said metering valve means to be partially opened while the damper means remains closed and for opening said damper means only after said metering valve has been opened to a predetermined extent, said damper means comprising a flat generally rectangular damper body, a leading edge portion bent at an obtuse angle with respect to said body and a following edge portion bent at an obtuse angle with respect to said body; said edge portions being bent in opposite directions with respect to said body.
 4. The improvement of claim 3 wherein said fuel inlet means includes a gaseous fuel supply line and a liquid fuel inlet line, the metering valve means comprising a valve in said gaseous fuel supply line and a second valve in said liquid fuel inlet line, said valves being coupled for concordant actuation.
 5. A linkage for coordinating the opening of an air damper in a burner with the opening of two fuel supply valves comprising shaft means coupled to said fuel supply valves for rotation corresponding to opening and closing motion of the valves, crank means fixed on said shaft means, a linking rod pivotally secured at one end to said crank means, the other end of said linking rod being slidably and pivotally received in a slot defined in means fixed to said air damper for limited movement of said linking rod while the air damper remains stationary, one of said valves being actuated by the rotation of a member having a camming surface in contact with a piston of said one valve.
 6. The linkage of claim 5 wherein said means fixed to said air damper is an angle having a leg extending generally perpendicular to a body portion of said damper, said slot being defined in said leg.
 7. An air damper for a burner having a flat rectangular body, and two opposite edge portions integrally formed with said body and extending parallel to the axis of rotation of said damper, each said edge portion being bent to form an obtuse angle with respect to the plane of said body, said edge portions extending in generally opposite directions with respect to said body, and means secured to said body and having a leg extending generally perpendicular to said body, said leg means defining a slot extending generally perpendicular to said body. 